U.S. Pat. No. 3,837,704 discloses a lengthwise-adjustable, compressed-gas-filled gas spring, particularly for continuous height adjustment of chairs, seats, tables, or the like, with two cylinders mounted coaxially one inside the other, and with a piston displaceably mounted in the inner cylinder, said piston being provided with a seal resting against the inside wall of the inner cylinder which divides the internal chamber of the inner cylinder into two housing chambers. The piston is connected with a piston rod, which emerges from one end of the cylinder in a sealed manner. The housing chamber on the piston rod side is always connected by at least one opening with the annular chamber between the cylinders and with a valve which is provided at the opposite end. The valve serves to connect or separate the other housing chamber with or from the annular space via at least one passageway. In this case, a valve pin is provided in the sealing plug of the outer cylinder and the inner cylinder at the end opposite the piston-rod end. The valve pin is capable of being pushed into the gas spring to connect the housing chamber with the annular chamber.
The inside of the sealing plug is provided with a bore with a slightly larger diameter than the cylindrical part of the release pin and an expansion of the bore to accept a seal. A bypass chamber is provided, connectable with this inside part of the sealing plug, said chamber being connected on one side via a bore in the inside part with the cylindrical annular chamber and on the other side via a connecting chamber which is formed when the actuating pin is pushed in between the annular groove of the latter and the inside wall of the seal. In this known lengthwise-adjustable gas spring a sprecial valve is therefore provided at one end.
This lengthwise-adjustable gas spring has proven excellent in practice.